MDL-54573 testing: use dbtype rather dbvendor for diagnostics

So that we can differentiate between drivers

lib/testing/classes/util.php

@@ -1103,7 +1103,7 @@ abstract class testing_util {
         $env['phpversion'] = $phpversion;
 
         // Add database type and version.
-        $dbtype = $DB->get_dbvendor();
+        $dbtype = $CFG->dbtype;
         $dbinfo = $DB->get_server_info();
         $dbversion = $dbinfo['version'];
         $env['dbtype'] = ucfirst($dbtype);